1. Field of the Invention
The present invention relates to an active matrix panel, a detection apparatus and a detection system.
2. Description of the Related Art
An active matrix panel having an array of pixels (pixel array) including switching elements, such as thin film transistors (TFTs) is manufactured using a thin film semiconductor manufacturing technology. In recent years, in the active matrix panel, a system-on-panel design is required to be adopted. This design involves integrally forming drive circuits, such as gate driver circuits, on a substrate in a TFT process. Particularly, for a detection apparatus having an array of pixels (pixel array) where a switching element and a conversion element, such as a photoelectric conversion element, are combined, the system-on-panel design is required in order to reduce the pixel pitch, the number of components and the border width. The system-on-panel-type gate driver circuit used for such a detection apparatus has the following technical problems.
(1) Function of Switching the Number of Driving Gate Lines
A drive circuit sequentially applies a voltage (conducting voltage) for making pixel TFTs connected to one to a several gate lines be conductive. In the case where the number of gate lines to be driven at one time is one, the mode is a normal (high resolution) mode. In the case where the number is plural, the mode is a pixel addition (high sensitive) mode, in which light signal charges of pixels are added. Particularly, in a radiation detection apparatus, these modes can be switched to acquire optimal images while radiation exposure doses to patients are suppressed.
(2) Stabilization of Gate Line Potential During non-selected Period
Even in a time period where a conducting voltage is applied to a certain gate line, no conducting voltage is applied to most of gate lines. When the gate lines come into a floating state, the voltage of the gate line varies owing to capacitance coupling with a signal line and external electromagnetic fields, thereby reducing readout image quality. Particularly, an active matrix panel for a radiation detection apparatus has gate lines about three times as many as those of a display device, while measuring the charge amount of pixels at high resolution. Accordingly, it is particularly important to stabilize the gate line voltage during a time period (non-selected period) where no conducting voltage is applied.
U.S. 2008/0316156 discloses a drive circuit for a liquid crystal display device (LCD) as a circuit that solves problems analogous to the above problems. The drive circuit is formed as single-conducting TFT integrally with a substrate. The drive circuit in U.S. 2008/0316156 includes a shift register and a scan voltage generation circuit. The scan voltage generation circuit functions as a demultiplexer that branches the output voltage of the shift register into a plurality of gate lines. The number of gate lines driven at a time can be changed by controlling the timing of clocks to be provided to a scan voltage generation circuit. The shift register can output not only a main output signal (first shift pulse voltage) but also a complementary output signal thereof (second shift pulse voltage). Through use of these signals, during the most of the non-selected period, the gate lines are connected to a DC power source and the floating state of the gate line can be avoided.
However, since the shift register in U.S. 2008/0316156 outputs two types of output signals, which are the first and second shift pulses, this register has a complicated circuit configuration. The shift register in U.S. 2008/0316156 includes 18 TFTs for each unit circuit. Even if redundant TFTs, such as Tr1 and Tr2 in FIG. 4 in U.S. 2008/0316156 are counted as one TFT, the register includes 10 TFTs for each unit circuit. The drive circuit with such a complicated circuit configuration has a large layout area, and causes reduction of manufacturing yield.
The present invention has an object to reduce the layout area of a drive circuit for gate lines in an active matrix panel and improve the manufacturing yield.